This invention relates in general to processing drums and more specifically, to a process for machining hollow cylinders.
In the art of electrophotography an electrophotographic imaging member comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the imaging surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated area. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electrostatically attractable toner particles on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
Electrophotographic imaging members having a drum configuration are usually multilayered photoreceptors that comprise a rigid hollow rigid cylindrical substrate having a conductive layer, an optional hole blocking layer, a charge generating layer, and a charge transport layer. These layers are usually formed by a coating process such as dip coating or spraying. Excellent toner images may be obtained with these multilayered drum photoreceptors.
During image cycling in a copier, printer or duplicator, the outer surface including the ends of the drums must meet critical tolerance requirements to avoid contact with closely spaced devices such as charging and developing applicator rolls. Accidental contact with these closely spaced devices form undesirable grooves that degrade images formed during image cycling.
These drums are usually supported with the aid of end caps which are mounted at each end of the drum. The end caps are, in turn, supported for rotation by any suitable device such as a shaft extending through the end caps or by molded-in or machined shafts extending out from the centerline of the caps. These shafts are supported by any suitable member of a machine frame. The shafts may be fixed to the machine frame and stationary with the drum rotating around the shaft or may be fixed to the end caps for rotation with the drum. Since the drums are normally formed by extrusion processes, they have imperfect dimensions and require machining to meet the high tolerance requirements of precision devices. Machining may involve removal of material from the inside surface of the ends of the drum to facilitate precise positioning of the end caps; cutting of the ends of the drums to achieve the required drum length; and/or chamfering of the ends of the drum to promote installation of the end caps. In subsequent operations, the outside surface of the drum is usually lathed to ensure roundness, avoid conicity and form a mirror finish.
Thus, in modern imaging systems, the tolerance requirements for drum to charger or applicator roll spacings are extremely high to avoid poor image quality characteristics.
Machining of the end of a hollow metal cylinder or drum to alter length or to chamfer is well known and involves mounting the cylinder in a holder and bringing a spindle carrying a rotatable cutting head into contact with the end of the drum. The cutting head carries at least one cutting tool. Preferably, the rotatable cutting head is rotated by a high precision electric motor free of vibrations. While the cutting head is being rotated, an edge of the cutting tool is brought into contact with one end of the stationary drum to remove material from the drum. The edge of the cutting tool is moved completely around the end of the drum by the rotating cutting head to remove material from the drum end for drum length alteration, and/or to form a chamfer (bevel), and/or to bore the inner surface of the drum at the end of the drum. The cutting tool is normally incremented in relationship to the end of the drum by movement of the rotating head toward the drum in a direction parallel to the imaginary axis of the drum. Thus, the end cutting, chamfering and boring may be accomplished simultaneously or in separate sequential cutting operations.
This machining of predetermined portions of the ends of drums is usually accomplished manually with the rotating cutting tool continuously bathed with an expensive cutting liquid. The cutting tool is usually a carbide tool. This carbide tool requires frequent sharpening. Resharpening requires shut down of the machining operation, removal of the carbide tool, sharpening of the tool, and reinstallation of the tool. Because of the mist and chips produced during machining, the apparatus must be enclosed in a housing to prevent cutting fluid mist from contaminating other operations or soaking the machine operator. For operator access, the housing is usually fitted with a safety door. Although the cutting liquid helps remove chips from the drum and cutting tool, reduces surface tearing, and cools the cutting bit and drum during machining, operators must continuously remove large amounts of chips that have adhered to or become tangled around the cutting tool as well as other chips which accumulate in the work area. This accumulation creates premature component failure in subsequent processing operations. In addition, some of the chips and cutting liquid deposit on the interior surface of the hollow drum. Loading and unloading of drums from the machining fixture for every machining cycle requires opening and closing of the door in the machining apparatus housing and manual mounting and dismounting of the drums from the machining fixture. This activity often presents safety and ergonomic concerns such as repetitive motion disabilities, e.g. tendonitous. Moreover, frequent contact between airborne cutting liquid mist and the operator often leads to dermatitis. Further, spillage of cutting liquids on the floor adjacent the machining devices pose additional safety issues. After subjecting the drum to a chamfering and/or end cutting operation, the cutting liquid and chips must be washed off the interior and exterior surfaces of the drum with hot water and allowed to dry before the substrate can be lathed to form a mirror surface on the exterior of the drum. The lengthy drying takes place at ambient temperature and requires up to about 24 hours. If the cutting liquid and chips from the end cutting and chamfering operations are not removed from the interior of the drum, they contaminate coating baths during subsequent coating operations. The contaminated coating baths lead to defects in the deposited coatings and coating operation shut down is necessary to replace the contaminated coating material.
Foam dampening plugs are inserted in interior of the substrates prior to the lathing operation. Since the drum is usually very thin, lathing of a drum without a foam rubber dampening plug causes the drum to vibrate during lathing thereby causing the formation of a "barber pole" pattern which adversely affects electrophotographic images formed on the final drum. These dampening plugs are not compatible with a wet or damp surface because they swell upon exposure to the cutting liquid present on the interior surface of the drum and cannot subsequently be inserted into the interior of fresh drums to be lathed because the swollen outside diameter of the plug has become greater than the inside diameter of the drum. Also, repeated exposure to cutting liquid and chips causes deterioration of the dampening plug material. Thus, the cutting liquid and chips must be 1 washed off the interior and exterior surfaces of the drum with hot water and allowed to dry before the substrate can be lathed. Substrate drying time can require up to 24 hours. Further, if material is removed from a drum substrate by a machining processes using a cutting liquid, the handling and disposal of the liquid presents difficulties from the environmental impact point of view. Also, liquid removal processes require elaborate and expensive equipment and are time intensive. Thus, these liquid removal and cleaning techniques fail to provide satisfactory photoreceptor substrates. Moreover, throughput of the product of the aforesaid processes is undesirably low.